1. Field of the Invention
This invention relates to a radiation image recording and read-out method wherein a recording material provided with a stimulable phosphor layer is exposed to radiation, which causes a radiation image to be stored thereon, and is thereafter exposed to stimulating rays, which cause the recording material to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation, with the emitted light then being detected and converted into an electric signal. This invention particularly relates to a radiation image recording and read-out method wherein a recording material capable of being stimulated by stimulating rays having comparatively long wavelengths is used. This invention also relates to an apparatus for carrying out the radiation image recording and read-out method.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store part of the energy of the radiation. Then, when the phosphor which has been exposed to radiation is exposed to stimulating rays such as visible light, the phosphor emits light in proportion to the amount of energy stored thereon during its exposure to the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a recording material provided with a layer of the stimulable phosphor is first exposed to radiation which has passed through an object, such as the human body, which causes a radiation image of the object to be stored thereon, and is then exposed to stimulating rays, which cause the recording material to emit light in proportion to the amount of energy stored thereon during its exposure to radiation. The light emitted by the recording material upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The electric image signal is processed and used in order to reproduce a visible image which has good image quality and can serve as an effective tool in, particularly, the efficient and accurate diagnosis of an illness.
The recording material provided with the stimulable phosphor layer takes on the form of, for example, sheets, panels, drums, or endless belts. (Such a recording material will hereinafter be referred to as a stimulable phosphor sheet.)
In the radiation image recording and reproducing systems described above, the finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). Also, the stimulable phosphor sheet is used to store the radiation image temporarily, and the final visible image is reproduced on a final recording medium. For reasons of economy, therefore, it is desirable for the stimulable phosphor sheet to be reusable.
Further, a mobile X-ray diagnostic station, e.g. a bus serving as such, may be provided with a radiation image recording and read-out apparatus using stimulable phosphor sheets. In cases where such a mobile X-ray diagnostic station moves from place to place so that mass medical examinations may be recorded, it is disadvantageous to have to load the mobile X-ray diagnostic station with a large number of stimulable phosphor sheets, and therefore the number of stimulable phosphor sheets which can be carried along with the mobile X-ray diagnostic station is limited. Therefore, it is desirable that a small number of reusable stimulable phosphor sheets be carried along with the mobile X-ray diagnostic station, and that the stimulable phosphor sheets be circulated and reused for the recording and read-out of radiation images. With such a mobile X-ray diagnostic station, radiation image signals representing the images of many objects can be obtained. Also, if the stimulable phosphor sheets are circulated and reused, the recording of radiation images can be conducted continuously, and it becomes possible to increase the speed with which radiation images are recorded in mass medical examinations. This is very advantageous from the point of view of practical use.
In order for stimulable phosphor sheets to be reusable in the manner described above, energy remaining on the stimulable phosphor sheets after they have been exposed to stimulating rays during the readout of radiation images therefrom should be erased with the method disclosed in, for example, U.S. Pat. No. 4,400,619 or Japanese Unexamined Patent Publication No. 56(1981)-12599. The erased stimulable phosphor sheet can then be reused to record a radiation image.
In order to accomplish the aforesaid purpose, it is desirable that there be combined into a single apparatus: at least a single recording material which is provided with a stimulable phosphor layer and which can be circulated and reused, an image recording section for exposing the recording material to radiation which has passed through an object, an image read-out section for reading out the radiation image stored on the recording material, and an erasing section for erasing energy remaining on the recording material after the radiation image has been read out. A mobile X-ray diagnostic station allows medical examinations to be carried out at different locations, and the aforesaid apparatus is easy to load into such a mobile diagnostic station. Such an apparatus can easily be located in a hospital, or the like. This is very advantageous for practical use.
Accordingly., the applicant proposed in, for example, U.S. Pat. No. 4,543,479, a builtin type of radiation image recording and read-out apparatus which comprises an image recording section, an image read-out section, and an erasing section. At least a single recording material is secured to a support material, and the support material is circulated and moved with respect to the image recording section, the image read-out section, and the erasing section. The applicant also proposed in, for example, U.S. Pat. No. 4,851,679, a built-in type of radiation image recording and read-out apparatus comprising an image recording section, an image read-out section, and an erasing section which are located along a predetermined circulation path. A plurality of stimulable phosphor sheets which can be moved independently of one another are employed as recording materials. The stimulable phosphor sheets are sequentially moved along the circulation path and circulated through the image recording section, the image read-out section, and the erasing section. With the built-in type of radiation image recording and read-out apparatuses, a recording material (i.e. a stimulable phosphor sheet) can be reliably circulated and reused in the recording of a radiation image.
Nowadays there is a need for a built-in type of radiation image recording and read-out apparatus which is small in size and inexpensive. In order to satisfy this need, an attempt has been made to employ a semiconductor laser as the source for the stimulating rays in the image read-out section of a built-in type of radiation image recording and read-out apparatus. This is because semiconductor lasers are comparatively small in size and inexpensive. Among the various types of semiconductor lasers, the semiconductor laser which has the largest output power produces a laser beam having wavelengths falling within the range of 680 nm to 830 nm, the wavelengths of which range are longer than the wavelength (633 nm) produced by an He-Ne laser, or the like. He-Ne lasers have heretofore been used widely as the source of stimulating rays for stimulating the stimulable phosphors used in conventional recording materials. Therefore, the semiconductor laser which has the largest output power is not suitable for stimulating the stimulable phosphors used in conventional recording materials because of the long wavelengths it produces.